1. Field of the Invention
This invention relates to a magnetic disk drive for a cartridge assembly including a magnetic disk, and, more particularly, to a disk drive capable of neutralizing or dissipating an accumulation of static electricity carried by the cartridge assembly.
2. Description Relative to the Prior Art
A conventional cartridge, such as used with this invention, includes a magnetic disk rotatably disposed within a dual-sided jacket. The magnetic disk has a central hub that is revealed to drive apparatus through a central opening in both sides of the jacket. The jacket further contains two aligned windows through which a magnetic transducer may extend for magnetically interfacing with either surface of the disk as the disk is rotatably driven. A liner is ordinarily provided on the inner surfaces of the jacket adjacent the disk for reducing friction between the jacket and the disk and for capturing contaminants on the disk. In addition, the liner has an irregular surface which reduces the tendency of the disk to adhere to the plastic jacket when a static charge is present on the jacket.
A plastic, impact-resistant material, such as acrylonitrile butadiene styrene (ABS), has been found particularly suitable for forming the jacket of a cartridge. Such plastic materials, however, possess very high electrical resistances (e.g., 3.7.times.10.sup.15 ohms-cm for ABS) and collect large accumulations of static electricity due to normal handling. Such accumulations of static electricity may induce a spurious signal as the static discharges through the transducer. The general approach to this problem has been to provide a conductive element that helps to dissipate or neutralize the charge before it can discharge through the transducer. For instance, in U.S. Pat. No. 4,038,693 an electrically conductive layer is provided on the inside surface of the jacket. As another example, a conductive outrigger is provided on a transducer in U.S. Pat. No. 4,058,846 so as to ground any electrostatic charge on the surface of the disk. The drive apparatus may also be modified, as shown in U.S. Pat. No. 4,040,105, to include an electrically conductive, flexible skirt hung in contact with an outer surface of the jacket for draining off an electrostatic charge accumulation. The skirt lies on the same side of the jacket as does the transducer so as to be particularly effective in diverting or intercepting charge before it reaches the transducer and produces a spurious signal.
These approaches to static elimination are incorporated in systems employing a magnetic interface that requires either a pair of abbutting transducers or a pressure pad opposite a single transducer in order to maintain contact between the operating transducer and the disk. Unlike these approaches, the object of the present invention is to neutralize an accumulation of static on a cartridge assembly used in a single-sided interface, that is, a system in which the disk is aerodynamically drawn to the transducer without the intervention of a pressure pad or an opposing transducer. Static presents a special problem in relation to such a system. In particular, an accumulation of static will attract the disk to the inner surface of the jacket opposite the transducer. Often the attractive electrostatic forces are sufficient to overcome the aerodynamic coupling forces and the disk pulls away from the transducer and, in the worst case, sticks to the inner surface of the jacket opposite the transducer. The anti-static solutions heretofore disclosed are not designed to operate in such an interface.